The purpose of this project is to analyze the hormonal control of calcium metabolism durng pregnancy, intra-uterine growth, and post-natal development. In particular, these studies focus on the role of the vitamin D-endocrine system. An important role of vitamin D is suggested by developmental alterations in vitamin D metabolism and action, by the presence of vitamin D-dependent calcium binding protein (CaBP or calbindin-D) in placenta and yolk sac, and by the presence of calcitriol receptors and calcitriol synthesis in placenta. Recent studies have revealed that the post-natal appearance of intestinal CaBP is accelerated by epidermal growth factor (EGF). Experiments are planned to define the molecular mechanism of EGF's effect on CaBP accumulation and its role in calcium homeostasis in both young and mature animals. The mechanims for control of CaBP gene expression during development are poorly understood. To begin to address this problem, mouse CaBP cDNA probes will be isolated and sequenced. cDNA (and RNA) probes will be used to characteize CaBP mRNA accumulation and CaBP gene transcription (a) in placenta and yolk sac during gestation, (b) in kidney and intestine during early post-natal life, and (c) uterus following estrogen administration. Experiments are planned to define the development abnormalities of CaBP in tissues of the Gy hypophosphatemic mouse and the oc osteopetrotic mouse. A potential clue to the mechanism of placental calcium transport is the finding of CaBP in cells that line the endodermal sinuses of mouse placenta. Experiments are planned to determine (by in situ hybridization) the cellular localization of CaBP mRNA in murine placenta and to define, both in vivo and in vitro, the hormonal control of placental CaBP content. The development expression and cellular localization of CaBP and its mRNA in human placenta will also be determined. Human CaBP will be purified and sequenced, anti-CaBP antibodies will be produced, and human CaBP cDNA will be isolated and sequenced. Studies of human placenta will be accomplished using these tools for immunossay, immunohistochemistry, in situ hybridization, and mesurement of calbinding (CaBP) mRNA content. These studies will increase our understanding of developmental aspects of mammalian calcium transport and provide tools to study their pathological alterations.